In a known variable stroke engine, a piston is connected to a crankshaft via a plurality of links, and one of the links is connected to an eccentric portion provided on a control shaft supported by an engine main body via a control link so that the position of the end of the control link supported by the engine main body may be changed by turning the control shaft and the piston stroke may be thereby changed in a continuous manner. See Japanese patent laid open publication No. 2006-177192 and Japanese Patent Laid Open Publication No. 2003-322036.
In such a variable stroke engine, because the link mechanism required for varying the stroke of the piston is highly complex and an actuator is required for driving the control shaft, the size of the engine, in particular the lateral width of the engine as seen from the crankshaft end tends to be larger than those of comparable conventional engines. Therefore, because of the need to mount the engine in the engine room so as to avoid an interference with the output shaft for transmitting the engine output to the wheels, the engine room is required to be larger than desired to accommodate the engine. In particular in case of a FF (front engine, front wheel drive) car in which the engine is disposed in the engine room with the crankshaft oriented in a lateral direction, because of the need to avoid the interference with the half shaft for driving the front wheels, it is difficult to reduce the size of the engine room.
A starter motor is typically mounted on one side of the engine main body, and this starter motor drives a flywheel (ring gear) when starting the engine. In a variable stroke engine, it is important to determine the positioning of a starter motor so as not to interfere with various link members that form a variable stroke link mechanism.
In such a variable stroke engine, because of the presence of the control shaft and control link, one of the side walls of the engine main body (typically consisting of a cylinder block) substantially bulges out as seen from the axial direction of the crankshaft. Therefore, when a starter motor is installed without any layout consideration, the freedom in the design of the link geometry (layout of the control shaft and control link) may be impaired, and the engine may fail to be properly mounted in the engine room of the motor vehicle.
When the actuator of such a variable stroke engine is heated to a high temperature owing to the heat of the exhaust manifold or the like, various problems may be created. It is proposed in Japanese patent laid open publication No. 2006-177192 to control the rise in the temperature of the actuator by placing the actuator on the exterior of the engine so that the flow of air from the front part of the vehicle owing to the motion of the vehicle may be effectively directed to the actuator and as far away from the exhaust manifold as possible. However, the arrangement disclosed in Patent Japanese patent laid open publication No. 2006-177192 is not able to adequately prevent the rise in the temperature of the actuator, and there is a need to more effectively protect the actuator from heat. Also, the freedom in the layout of the actuator was limited.